Symptoms

The female sawflies lay eggs in soft young rose stems. The stems often split open where the eggs were laid, resulting in elongate scars

Whitish green, caterpillar-like larvae with black spots and yellow blotches cause extensive defoliation in early and late summer

‹

›

Elongated scars on stems are caused by the female sawflies laying eggs in the shoots and flower stalks. The larvae cause extensive defoliation in early and late summer, as they feed on the leaves and shoots.

Control

Non chemical

The larvae can be removed by hand. If eggs are present in the stem these can also be destroyed.

Chemical control

If infestations are too heavy for hand picking, control may be achieved by spraying with pesticides. Spaying at dusk is likely to give the best results

Organic pesticides, such as those containing pyrethrum (e.g. Bug Clear Gun for Fruit and Veg, Defenders Bug Killer, ecofective Bug Killer) will control young larvae but larger larvae are more tolerant of these insecticides

Biology

In Britain there are two species of large rose sawfly: Arge pagana and A. ochropus. The adult insects of both species have yellow abdomens with the legs, thorax and heads being mostly black. Arge pagana is the more common species.

Rows of eggs are inserted into soft young rose shoots and female sawflies are sometimes seen dangling from such stems, attached only by their saw-like egg-laying organs.

After hatching, the larvae feed together in family groups. They are pale green with black spots and yellow blotches, and are up to 25mm (about 1in) long. When fully fed, they go into the soil to pupate.

The large rose sawfly (Arge pagana) will produce two (sometimes three) generations from May to October. Arge ochropus usually has a single generation in early summer, but sometimes there is a second generation in late summer.